The Use Of Flue Gas And Several Flocculants For Harvesting Energy Microalgae

The Microalgae has been considered as one of the most promising feedstock of biofuels, and the bottleneck of microalgal biofuels production is the cost. The cost of harvesting microalgae could be reduced by the method of flocculation. Serval flocculants were studied in this paper, and a new method of flocculation by using flue gas was also studied.In the first chapter, flocculation of microalgae with chitosan, polyacrylamide, Al2（SO4）3, NaOH and HNO3 was evaluated. Their flocculation efficiencies and optimal dosages were discussed. The effects of the flocculants on cells viability were also investigated and the cells were found to be intact during the flocculation process. Moreover, the effects of flocculants on the extractions were evaluated. Lipid content after flocculants treatments showed no significant differences. Carbohydrate content was lower but protein content was higher after NaOH treatment than those after other treatments. Furthermore, the five flocculated media maintained approximate growth yields to that of the fresh medium in microalgal cultivation, indicating the five flocculated media could be recycled, thereby reducing the cost of biodiesel production from microalgae. Finally, economic comparison of the flocculants was made and the cost of using HNO3, including flocculating cells and recycling medium, was found to be the lowest.Using flue gas as flocculant for harvesting microalgae was studied in the second chapter. Base on the flocculant of HNO3, the cheap and convenient chemical, the acidic gases of flue gas was used for flocculating microalgae. The flocculation performances and the effects of biomass concentration were evaluated, and the flocculation efficiencies of flue gas for both species of microalgae reached over 90%. Moreover, the side effect on microalgal cells viability was not significant.In addition, most SO₂ of flue gas was absorbed by the algal solution and the absorptivity reached 95⁹8%. Furthermore, using the residual gas after flocculation for the cultivation of fresh microalgae was proved to be feasible. Therefore, using flue gas as flocculant for harvesting microalgae could turn the waste into wealth with high flocculation efficiency, reducing the cost and clean the flue gas for microalgae cultivation, which meant it was an efficient, environmentally friendly and more economic choice.